Re: [PATCH v7 13/36] drm: msm: fix common struct sg_table related issues

[Rob Clark <robdclark@gmail.com>]

On Fri, Jun 19, 2020 at 3:37 AM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> The Documentation/DMA-API-HOWTO.txt states that the dma_map_sg() function
> returns the number of the created entries in the DMA address space.
> However the subsequent calls to the dma_sync_sg_for_{device,cpu}() and
> dma_unmap_sg must be called with the original number of the entries
> passed to the dma_map_sg().
>
> struct sg_table is a common structure used for describing a non-contiguous
> memory buffer, used commonly in the DRM and graphics subsystems. It
> consists of a scatterlist with memory pages and DMA addresses (sgl entry),
> as well as the number of scatterlist entries: CPU pages (orig_nents entry)
> and DMA mapped pages (nents entry).
>
> It turned out that it was a common mistake to misuse nents and orig_nents
> entries, calling DMA-mapping functions with a wrong number of entries or
> ignoring the number of mapped entries returned by the dma_map_sg()
> function.
>
> To avoid such issues, lets use a common dma-mapping wrappers operating
> directly on the struct sg_table objects and use scatterlist page
> iterators where possible. This, almost always, hides references to the
> nents and orig_nents entries, making the code robust, easier to follow
> and copy/paste safe.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

Acked-by: Rob Clark <robdclark@gmail.com>

(let me know if you want me to take this one in via msm-next or if the
plan is to take the series via drm-misc)


> ---
>  drivers/gpu/drm/msm/msm_gem.c    | 13 +++++--------
>  drivers/gpu/drm/msm/msm_gpummu.c | 14 ++++++--------
>  drivers/gpu/drm/msm/msm_iommu.c  |  2 +-
>  3 files changed, 12 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> index 38b0c0e1f83e..e0d5fd36ea8f 100644
> --- a/drivers/gpu/drm/msm/msm_gem.c
> +++ b/drivers/gpu/drm/msm/msm_gem.c
> @@ -53,11 +53,10 @@ static void sync_for_device(struct msm_gem_object *msm_obj)
>         struct device *dev = msm_obj->base.dev->dev;
>
>         if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
> -               dma_sync_sg_for_device(dev, msm_obj->sgt->sgl,
> -                       msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
> +               dma_sync_sgtable_for_device(dev, msm_obj->sgt,
> +                                           DMA_BIDIRECTIONAL);
>         } else {
> -               dma_map_sg(dev, msm_obj->sgt->sgl,
> -                       msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
> +               dma_map_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);
>         }
>  }
>
> @@ -66,11 +65,9 @@ static void sync_for_cpu(struct msm_gem_object *msm_obj)
>         struct device *dev = msm_obj->base.dev->dev;
>
>         if (get_dma_ops(dev) && IS_ENABLED(CONFIG_ARM64)) {
> -               dma_sync_sg_for_cpu(dev, msm_obj->sgt->sgl,
> -                       msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
> +               dma_sync_sgtable_for_cpu(dev, msm_obj->sgt, DMA_BIDIRECTIONAL);
>         } else {
> -               dma_unmap_sg(dev, msm_obj->sgt->sgl,
> -                       msm_obj->sgt->nents, DMA_BIDIRECTIONAL);
> +               dma_unmap_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);
>         }
>  }
>
> diff --git a/drivers/gpu/drm/msm/msm_gpummu.c b/drivers/gpu/drm/msm/msm_gpummu.c
> index 310a31b05faa..319f06c28235 100644
> --- a/drivers/gpu/drm/msm/msm_gpummu.c
> +++ b/drivers/gpu/drm/msm/msm_gpummu.c
> @@ -30,21 +30,19 @@ static int msm_gpummu_map(struct msm_mmu *mmu, uint64_t iova,
>  {
>         struct msm_gpummu *gpummu = to_msm_gpummu(mmu);
>         unsigned idx = (iova - GPUMMU_VA_START) / GPUMMU_PAGE_SIZE;
> -       struct scatterlist *sg;
> +       struct sg_dma_page_iter dma_iter;
>         unsigned prot_bits = 0;
> -       unsigned i, j;
>
>         if (prot & IOMMU_WRITE)
>                 prot_bits |= 1;
>         if (prot & IOMMU_READ)
>                 prot_bits |= 2;
>
> -       for_each_sg(sgt->sgl, sg, sgt->nents, i) {
> -               dma_addr_t addr = sg->dma_address;
> -               for (j = 0; j < sg->length / GPUMMU_PAGE_SIZE; j++, idx++) {
> -                       gpummu->table[idx] = addr | prot_bits;
> -                       addr += GPUMMU_PAGE_SIZE;
> -               }
> +       for_each_sgtable_dma_page(sgt, &dma_iter, 0) {
> +               dma_addr_t addr = sg_page_iter_dma_address(&dma_iter);
> +
> +               BUILD_BUG_ON(GPUMMU_PAGE_SIZE != PAGE_SIZE);
> +               gpummu->table[idx++] = addr | prot_bits;
>         }
>
>         /* we can improve by deferring flush for multiple map() */
> diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
> index 3a381a9674c9..6c31e65834c6 100644
> --- a/drivers/gpu/drm/msm/msm_iommu.c
> +++ b/drivers/gpu/drm/msm/msm_iommu.c
> @@ -36,7 +36,7 @@ static int msm_iommu_map(struct msm_mmu *mmu, uint64_t iova,
>         struct msm_iommu *iommu = to_msm_iommu(mmu);
>         size_t ret;
>
> -       ret = iommu_map_sg(iommu->domain, iova, sgt->sgl, sgt->nents, prot);
> +       ret = iommu_map_sgtable(iommu->domain, iova, sgt, prot);
>         WARN_ON(!ret);
>
>         return (ret == len) ? 0 : -EINVAL;
> --
> 2.17.1
>

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